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The invention relates generally to a pressure control system for a pneumatic offload. More particularly, the invention relates to a pressure control system for accurately controlling the air pressure in a discharge line during a pneumatic offload of a dry bulk good from a tank truck.
A dry bulk good, for example cement powder or plastic pellets, is often loaded into the tank of a tank truck and transported from the manufacturer to a customer. At the destination, the dry bulk good is unloaded from the tank utilizing a pneumatic offload process. The dry bulk good, also referred to herein as the product, is offloaded from the tank truck through a discharge line attached to a coupler provided on the underside of the tank. A blower positioned upstream of the coupler is used to initiate, facilitate and expedite the pneumatic offload process. Specifically, the blower directs ambient air into the discharge line, and thereby produces a positive pressure in the discharge line. The positive pressure of the air in the discharge line moves the product out of the tank through the discharge line to a receptacle, such as a silo, for receiving the dry bulk good.
Accurate control of the pressure of the air in the discharge line is required to optimize and maintain the flow of the product through the discharge line. If the pressure of the air in the discharge line is less than the optimum pressure, the time required to offload the product from the tank will be excessive or the product may plug the discharge line. A slow offload is inefficient and results in increased operating costs to the manufacturer and the customer. A plug in the discharge line requires manpower and results in down time to clear the discharge line and to restart the pneumatic offload process, which likewise results in increased operating costs to both the manufacturer and the customer. If the pressure of the air in the discharge line is greater than the optimum pressure, the back pressure in the discharge line can damage the blower, resulting in unnecessary manpower, expense and down time to remove and replace the blower. The product may also be damaged if the temperature or the velocity of the air in the discharge line becomes excessive during the pneumatic offload process.
As a result, the operator of the tank truck must pay careful attention to the pressure of the air in the discharge line. The pressure of the air is primarily a measure of the amount of restriction to the flow of the product through the discharge line. As such, the pressure of the air in the discharge line is a function of several variables including the operating speed of the blower, the temperature of the air in the discharge line, altitude, and the velocity of the air in the discharge line (i.e., the rate at which the product flows through the discharge line). Tank trucks are typically equipped with pressure gauges to assist the operator to monitor the pressure in the discharge line. However, if the operator does not continuously monitor the pressure gauges during the pneumatic offload process, or if any of the gauges provides a false reading, the time required to complete the offload process can be unacceptably extended, the blower can be damaged or the product can be compromised, as previously described. At present, the operator of the tank truck attempts to control the pressure of the air in the discharge line by constantly monitoring the pressure gauges, adjusting the operating speed of the blower and diverting the airflow of the blower into the tank truck or discharge line or venting the airflow to the ambient air through the blowdown line. However, the operating speed of the blower is relatively constant. Thus, adjusting the speed of the blower is an insufficient method of accurately controlling the pressure of the air in the discharge line.
In an attempt to protect the blower from damage, most tank trucks are equipped with a valve, commonly referred to as a xe2x80x9cpressure relief valve,xe2x80x9d for relieving the air pressure in the discharge line. The pressure relief valve relieves the air pressure in the discharge line by venting the air in the discharge line to the ambient atmosphere when the pressure of the air exceeds a predetermined pressure. Conventional pressure relief valves are commonly referred to as xe2x80x9cpop-offxe2x80x9d valves because the valve opens suddenly when the predetermined pressure is exceeded. However, there are at least two common characteristics of conventional pop-off valves that can cause serious problems during a pneumatic offload of a dry bulk good from a tank truck. First, because the valve opens suddenly, a large volume of air is rapidly vented from the discharge line to the ambient atmosphere. The rapid loss of a large volume of air causes the air pressure in the discharge line to drop significantly and quickly. As a result, the discharge line is susceptible to becoming plugged with the product. As previously mentioned, a discharge line that becomes plugged with product requires manpower and is time consuming to clear, thereby resulting in increased operating costs to the manufacturer and the customer, along with a corresponding loss of productivity.
Second, conventional pop-off valves are activated mechanically, and therefore, are not particularly accurate. As a result, the pop-off valve does not always open at a pressure that is sufficiently close to the predetermined pressure. The pop-off valve may open when the air pressure in the discharge line is actually less than the predetermined pressure, thereby resulting in a slower offload or a discharge line that becomes plugged with the product. In both instances, the manufacturer and the customer suffer increased operating costs, along with a corresponding loss of productivity. Conversely, the pop-off valve may not open until the pressure in the discharge line is actually greater than the predetermined pressure, thereby resulting in damage to the blower and the unnecessary expense and loss of productivity suffered to remove and replace the blower. Although adjustable pop-off relief valves are commercially available, they have a limited adjustment, and furthermore, cannot be readily or accurately adjusted in the field. Pressure control systems of the type commonly used in industrial manufacturing and laboratory environments utilize more accurate, electronically and mechanically activated pressure relief valves. However, the more accurate pressure relief valves currently available are not cost effective, reliable or durable enough for use in the field, and in particular, on a tank truck.
Presently, there is no commercially available pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload, and in particular, during a pneumatic offload of a dry bulk good from a tank truck. Furthermore, there is no commercially available pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload that is cost effective, reliable and durable enough for use in the field. Still further, there is no commercially available pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload that can be automatically activated and initialized from a remote location.
Thus, it is apparent that there exists a specific need for a pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload, and in particular, during a pneumatic offload of a dry bulk good from a tank truck. It is further apparent that there is a specific need for a pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload that is cost effective, reliable and durable. It is further apparent that there exists a specific need for a pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload that can be automatically activated and initialized from a remote location, for example from the cab of a tank truck or from a remote operating station via a satellite downlink.
Therefore, it is a principle object of the present invention to provide a pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload.
It is a more particular object of the invention to provide a pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload of a dry bulk good from a tank truck.
It is a further object of the present invention to provide a pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload of a dry bulk good from a tank truck that is cost effective to install and operate, and is reliable and durable enough for use in the field on a tank truck.
It is a further object of the present invention to provide a pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload that can be automatically activated and initialized from a remote location.
It is a more particular object of the invention to provide a pressure control system for accurately controlling the air pressure in a discharge line during a pneumatic offload of a dry bulk good from a tank truck that can be automatically activated and initialized from the cab of the tank truck or from a remote operating station via a satellite downlink.
The invention is a pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload. More specifically, the invention is a pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload of a dry bulk good from a tank truck. The pressure control system includes a supply of pressurized air, a blower in fluid communication with the ambient atmosphere and with the discharge line and a pressure relief valve in fluid communication with the supply of pressurized air and with the discharge line. Preferably, the blower of the pressure control system is operatively coupled to a power take off (PTO) from the engine of the tank truck. Furthermore, the pressure control system includes a breakover valve in fluid communication with the supply of pressurized air and with the pressure relief valve. The breakover valve is operatively positioned downstream of the supply of pressurized air and upstream of the pressure relief valve. Accordingly, the breakover valve prevents fluid communication between the supply of pressurized air and the pressure relief valve when the pressure of the supply of pressurized air is less than a predetermined minimum pressure required to operate the air brake system of the tank truck. The pressure relief valve is operatively positioned in the discharge line downstream of the blower. Thus, the pressure relief valve vents the air in the discharge line to the ambient atmosphere when the pressure of the air in the discharge line exceeds the pressure of the supply of pressurized air.
In the preferred embodiment, the pressure relief valve of the pressure control system includes a generally hollow valve body defining a valve chamber. The valve body has a first inlet port formed therein, a second inlet port formed therein and at least one outlet port formed therein. The pressure relief valve further includes a valve positioned within the valve chamber of the valve body and a valve seat is positioned opposite the valve for sealing engagement with the valve. The pressure of the supply of pressurized air biases the valve in the direction of the valve seat. Accordingly, the pressure relief valve vents the air in the discharge line to the ambient atmosphere through the first inlet port, the valve chamber and the outlet port when the pressure of the air in the discharge line exceeds the pressure of the supply of pressurized air biasing the valve in the direction of the valve seat. The pressure relief valve may further include a valve spring having a predetermined spring setting. The valve spring is positioned under compression within the valve chamber between the valve and the second inlet port for biasing the valve in the direction of the valve seat. Thus, the pressure relief valve vents the air in the discharge line to the ambient atmosphere through the first inlet port, the valve chamber and the outlet port when the pressure of the air in the discharge line exceeds the predetermined spring setting of the valve spring.
Preferably, the pressure control system further includes a first pressure regulator in fluid communication with the supply of pressurized air and with the pressure relief valve.
The first pressure regulator is operatively positioned downstream of the supply of pressurized air and upstream of the pressure relief valve. The first pressure regulator regulates the pressure of the supply of pressurized air to a first preselected pressure. The first preselected pressure biases the pressure relief valve in the closed position. Thus, the pressure relief valve vents the air in the discharge line to the ambient atmosphere when the pressure of the air in the discharge line exceeds the first preselected pressure. In another preferred embodiment, the pressure control system further includes a second pressure regulator in fluid communication with the first pressure regulator and with the pressure relief valve. The second pressure regulator is operatively positioned downstream of the first pressure regulator and upstream of the pressure relief valve and a solenoid valve is provided between the first pressure regulator and the second pressure regulator for engaging and bypassing the second pressure regulator. The second pressure regulator regulates the first preselected pressure to a second preselected pressure. The second preselected pressure biases the pressure relief valve in the closed position. Thus, the pressure relief valve vents the air in the discharge line to the ambient atmosphere when the pressure of the air in the discharge line exceeds the second preselected pressure.
In the preferred embodiment, a controller is electrically connected to the power take off (PTO) via a pneumatic switch and is further electrically connected to the solenoid. A temperature probe may be operatively positioned in the discharge line downstream of the blower for recording and reporting the temperature of the air in the discharge line and the controller may include a display for displaying the temperature recorded by the temperature probe. A vacuum probe may be positioned on the inlet side of the blower in addition to or in place of the temperature probe. The vacuum probe records and reports the negative pressure on the inlet side of the blower relative to the pressure of the air in the discharge line in the vicinity of the pressure relief valve. The display of the controller may likewise be configured to display the vacuum recorded by the vacuum probe. Similarly, the pressure control system may include an RPM sensor for recording and reporting the operating speed of the engine of the tank truck or the operating speed of the blower, an altimeter, manometer or barometer for recording and reporting the altitude of the tank truck relative to sea level at the time of the pneumatic offload, or an anemometer for recording and reporting the velocity of the air in the discharge line, and thus, the rate of flow of the product. Preferably, the controller is located in the cab of the tank truck remote from the supply of pressurized air, the blower and the pressure relief valve. The controller further preferably includes a relay for receiving an electrical command signal from a satellite downlink or other wireless communication system.